When is the blocking RNG called?

A while ago, I said:
----- Original Message -----
From: "Enzo Michelangeli" <em at who.net>
To: <gnupg-devel at gnupg.org>
Sent: Friday, November 24, 2000 2:57 PM
Subject: Re: When is the blocking RNG called?
[...]
> ----- Original Message -----
> From: "Sam Roberts" <sroberts at uniserve.com>
> To: "Enzo Michelangeli" <em at who.net>
> Cc: <gnupg-devel at gnupg.org>
> Sent: Friday, November 24, 2000 12:54 PM
> Subject: Re: When is the blocking RNG called?
[...]
> > Is it just a PRNG, or does it have a source of true/physical entropy
> > that it uses as a seed for a PRNG?
>> I believe it's a true RNG, but you may ask the product manager Gary Ellis
> <Gary.Ellis at dalsemi.com> . Official data sheets don't seem to be available
> yet (in Dalsemi, they tend to lag the actual product...).
Here is the answer from the iButton mailing list:
----- Original Message -----
From: "Don Loomis" <don.loomis at dalsemi.com>
To: <java-powered-ibutton at dalsemi.com>
Sent: Friday, December 29, 2000 4:59 AM
Subject: Re: [java-powered-iButton]How good is the RNG
> Jim Hurd wrote:
> >
> > What can you tell me about random number generation on the ibutton? Does
> > it have any sort of hardware entropy collection, or is it a pseudo
> > random number generator?
>> For the 1955 and 1957 it's a hardware based RNG that generates random
> data by measuring the difference in thermal noise between two fairly
> large (~10KOhm) resistors. For the older 1954 it's primarily a PRNG with
> small amounts of entropy contributed from the fastest moving bits of the
> RTC ripple counter.
>> Don
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